A mold is usually divided into two sides according to their function.
The side with the runner system is called injection side.
This side is not moved, therefore another common name is "fixed side".

The primary molding process mainly used in the plastic industry is injection molding.
With the help of the injection molding machine and the influence of heat, the plastic material is brought to a viscous state.
Subsequently, the melt is injected under pressure into the cavity in the mold.
The shape and surface structure is determined by the geometry of the cavity.
Cooling or cross-linking reaction (for elastomers) solidifies the part and it can be ejected after opening the two mold halves.

The injection molding process is particularly suitable for large quantities.
This is due to the fact of high mold costs which need to be payed proportionally by the produced parts.
Injection molded parts can be used directly after ejection.

A mold is usually divided into two sides according to their function.
The side with the ejector pins is called ejection side.
This side is moved for mold opening, therefore another common name is "movable side".

To orient the injection mold on the platen a locating ring is used.
The ring supports the mounting of the mold.
It helps to aligns the machine nozzle with the central length of the sprue bush.
With this, a good contact between the two elements is ensured.

Plates, which contain the part-cavity in the injection mold are called mold plates.
Usually there is one mold plate for the injection side and one for the ejection side.
Dependent on the complexity of the part, the cavity is carved directly into the mold plate or embeded with inserts into the mold plate.
The primary cooling system of the cavity is located in the mold plates as well.

A mold is usually divided into two sides according to their function.
The side, which is not moving during production is called fixed side.
This side contains the runner system, therefore another common name is "injection side".

A group of experts in the plastic industry founded the company PLEXPERT, 2006 in Germany, in order to save resources, providing a positive impact on budget and environment.
There are two divisions within the company. One is focusing on finite element simulations (FEM) like injection molding simulation and structural analysis.
Based on decades of practical experience DFM conform results are given by the consultant service of PLEXPERT to decrease part costs and increase quality in the production of plastic parts.
The second division is focused on the development and supply of soft- and hardware to the plastic industry. With the state of the art products PLEXPERT contributes to secure production and reduce the need of precious resources.
Today PLEXPERT has offices in Canada, Germany, Thailand and China in order to support its customers fast and effectively.
Due to a close network of plastic experts, partners are available in many other countries as well and offer PLEXPERT products and services.

For the production of injection molded parts a mold is necessary to be placed on the injection molding machine.
It is commonly build out of steel or aluminum and is designed as a permanent form.
Depending on the plastic material used millions of parts can be created with one mold.
The complexity of a mold range from a simple two-plate molds up to a complex stack mold with sliders, etc.
To avoid additional costs it is important to think about the mold concept early in the concept phase of part design.

In the mold, the correct temperature transfer between different materials is of crucial importance. The heat transfer inside the mold depends on a material depended-value, the heat transfer coefficient. The higher it is, the better is the transfer of the thermal energy from one material into the next one. As the hot runner system should transfer as little heat as possible to the remaining mold, an air gap helps to receive a small heat transfer coefficient, to get an isolated system.
It is necessary to know, that the heat transfer coefficient is no a constant value. It depends on material specific properties, like specific heat capacity, density and thermal conductivity, as well as geometry and roughness of the surface and for moving fluids on the flow behavior.

The transportation of the molten plastic from the injection unit through the mold to the cavity can be done by a hot runner system.
This consists of at least one sprue bushing, the manifold and one or more hot runner gates.
The single components are provided with heaters, which are controlled by suitable PID-Controllers, to achieve a uniform temperature distribution. The system, on the other hand, is thermally decoupled from the mold so that there is a homogeneous heat balance inside the hot runner system.
Advantages of a hot runner system are for example the saving of material and the reduction of the cycle time.

There are different versions of hot runner systems.
The simpliest is the hot runner system with thermal lock.
At the end of the injection and packing phase the melt is cooling down at the gate due to the heat transfer in the colder mold.
The viscosity of the plastc decreases and a "thermal lock" develops, which prevents the melt from entering into the cavity.

Hot runner systems with valve gates are commonly used.
A needle is added to the gates. It can be moved by cylinders (hydraulic or pneumatic) allowing or preventing the melt to enter the cavity.
Advantages of the usage of valve gates are the controllable filling of the parts and that the break-off point can be designed without a residual pin.

The injection molding process highly depends on temperature.
If the molten plastic enters the cavity the temperature is high and sequentially decreasing overtime.
The reduction in temperature is based on the given cooling layout of the mold and the process parameters set.
In simulation the temperature result shows temperature distribution of the part and mold at current instant.
It can help to evaluate temperature related aspects of the process, for instance, hot spot.

All melt channels together are called runner or runner system.
For these names, there is no distinction between hot and cold runner.
A good runner is responsible for a balanced filling of the cavity and less material and pressure loss.

The pressure of the melt pushes the mold to open due to a too low clamp force.
On the parting line, the mold opens a little and the outcoming melt freezes and a flash remains.
The risk of the flash formation can be reduced by the use of a machine with a higher clamp force or the reduction of the specific pressure in the cavity.
Another reason for flash formation can be the wrong positioning of the touching surfaces at the parting line.

In injection molding, during filling and packing phase the two mold halves are hold closed with the clamping force against the pressure of the melt. If the driving force of the cavity pressure is higher than the clamping force, the mold is pushed open by a few thousandths to hundreds of millimeters. This is known as the so-called mold breathing. Too large mold breathing can lead to flash formation, while too low mold breathing results to air compression with burn marks.
In order to optimize the required clamping force, dial gauges can be attached to the mold to determine the mold breathing. Permissible respiration depends on the quality requirements of the injection molded part, the material and the size of the machine.

An injection mold consists in general of two halves: injection side and ejection side.
The touching faces between these two halves are called parting line.
Through this, the air is transported from the cavity to the outside.
When the mold is opened, part and cold runner are separated from the mold at this line and ejected.
The parting line emerges in general as a surrounding seam on the part.

If the air can't escape, it will be compressed by the melt.
This leads to an increase in temperature and builds burn marks (black marks on the polymer).
A better venting or slower injection at lower temperatures can solve this issue in most cases.

To check if the parting line of the injection molding mold fit properly on each other inking is used.
This is done by applying inking-colour to one side of the mold (by spraying or brushing).
By closing and reopening the mold the colour is transferred to the other side of the mold.
Now it is easy to see where the mold fits exactly and where it does not.
This is an important information when it comes to subjects like short shot, flash formation or even multi-component molding.

The definition of quality according to DIN 55 350/T11 is "the nature of a unit as its suitability to meet specified and required needs".
Different factors are used to evaluate the quality of plastic parts.
The easiest is the optical evaluation.
Visible surfaces should not contain streaks, burn marks, sink marks and/ or air traps.
The dimensional examination is used to control the functionality of the part.
Shrinkage and Warpage are main quality criteria.
The technical drawing shows the necessary tolerances of the part for an acceptable quality.
Mechanical testings are necessary to check the different applied forces on the part dependent on its usage.
Fiber orientation, weld lines, voids and wall thickness may lead to this quality failure.
The choice of the material and the processing, both influence the mentioned quality factors decisively.
Injection molding simulation and additional structure analysis help to check the quality of a part in advance.